Process for recovery of poisonous gases in viscose manufacture



Patented Jan. 10, 1928.

UNITED STATES PATENT OFFICE.

FREDERICK CARL NIEDERHAUSER AND HAYDEN BENJAMIN KLINE, OF CLEVELAND, OHIO, ASSIGNORS TO THE INDUSTRIAL FIBRE COMPANY, OF CLEVELAND, OHIO.

PROCESS FOR RECOVERY OF IOISONOUS GASES IN VISCOSE MANUFACTURE.

N Drawing.

This invention has for one of its primary objects the ininimizingahnost to the point of prevention of the evolution of hydrogen sulfide gas in the normal process of viscose spinning without adversely afiecting the quality or characteristics of the modified cellulose produced therefrom, it having heretofore been practically impossible to economically absorb or otherwise render innocuous the hydrogen sulfide normally liberted during the process of spinning and specifically in the step of washing to neutrality the coagulated viscose filaments or films on account of the tremendous dilution with atmospheric air incident to the operation of the usual ventilating systems prevalent in viscose spinning rooms.

In this process to be described the hydrogen sulfide is caused to be evolved by decomposition of those bodies which give rise to hydrogen sulfide in the washing following the coagulation of the viscose, and in such a concentrated form and in such closed containers that itmay be economically treated to prevent the contamination of the air in the spinning room with hydrogen sulfide in the usual spinning steps.

More specifically, this process comprehends the treatment of viscose solutions before said solutions or the viscose contained in said solutions reaches the spinning room,

and while said viscose solutions are in a comparatively concentrated form and in substantially closed containers, said treatment being applied to the vi::cose at any desired stage of the process between the preparation of the crude viscose in the xanthal'ing drum up to the point where the viscose solution is regarded to be in optimum condition for 40 immediate spinning, that is, before the viscose solution has been coagulated, and hence before the viscose solution has reached the Y spinning room.

In the usual method of viscose manufacture, the viscose solutions are in cloted containers from the time of the commencement of the xanthating operation by the introduction of carbon bisulfide to matured alkalizcd cel-' lulose, through the step of dilution of the freshly prepared viscose with alkali hydroxide solutions, and through the various phases of viscose storage and ripening or maturing processes, and up to the point where the vis-- cose solution, matured to the point desired is forced through orifices into a congealing or Application filed March 9,

1927. Serial No. 174,090.

coagulating bath to be afterwards treated. 11"., therefore, a satisfactory process for obnoxious gases removal be applied to the viscose solution in this concentrated condition in a closed circuit, the efliciency of poisonous gas removal is greatly increased over a method aiming at the removal of the poisonous gases when diluted with exceedingly large volumes of air, such as normally exists in a spinning room. For instance, in the usual process of efficient ventilation in spinning rooms, quantitative determinations of hydrogen sulfide present in the atmosphere of saidrooms at various points and levels therein, seldom show more than one to two part-s hydrogen sulfide per million parts of air, and the usual practice is less than one part of hydrogen sulfide gas per two millions parts of air. This invent-ion comprehends the breaking down of the compounds normally present in a viscose solution and which give rise to the evolution of hydrogen sulfide subsequent to the coagulation of the same in the spinning step, and the'reridering innocuous such hydrogen sulfide compounds when liberated, and before they have an opportunity to contaminate the air of the spinning room or the atmosphere of other part of a viscose filament or film lant.

As is well known, in addition to possessing an odor disagreeable to many, hydrogen sulfide in the gaseous form exhibits a well marked toxicity on the human organism, and in comparatively small an'lounts, and this poisonous effect appears cumulative in its action so that a person may apparently show no effects of poisoning'by this gas when working in an atmosphere of the same for a long period, and then suddenly develop well marked symptoms, not diflicult to diagnose.

Furthermorethere is developed a certain idiosyncracy, ultra-sensitiveness or hypersensibility to the effects of this gas in some people, whereby they exhibit symptoms of poisoning in much below what has been roughly established by toxicologists as normal amounts which should produce untoward symptoms. For the above, and other reasons, many attempts have been made to eliminate this hazard and danger in rayon viscose manufacture, but as yet with only indifferent results. Normally in viscose production, the attempt is made toso dilute or attenuate the hydrogen sulfide gas evolved that it will be sufiiciently dilute to be harm less to the human organism when breathed for prolonged periods, and tall chimneys have been erected whereby the gas in the diluted form was spread over a large area, but such methods have been ineffective as shown by the darkening of houses in the neighborhood painted with lead paint, the blackening of hardware, enamels and utensils containing a metal or metals which produced a black or other colored sulfide. Fur thermore, notwithstanding the extreme dilution of hydrogen sulfide when disseminated as from a tall chimney, certain atmospheric conditions involving moisture may prevail, whereby large areas may show the effect of the gas upon paint and other materials and in a comparatively short time-such for instance, as over night. The effect of the gas upon the inhabitants of such a neighborhood is obvious.

In attempts to control or prevent the escape of hydrogen sulfide gas in viscose products manufacture, in one process the air from the spinning room has been passed through an ozonizing apparatus or system, but because in normal practice the amount of air to be thus treated in a given period of time is tremendous and excessive, and the rate of ozone is comparatively slow, and the process is expensive to install and operate, and furthermore, the sulfur of the hydrogen sulfide is probably oxidized to sulfuric acid, which is also a menace to the community.

Another method advocated by some is the absorption of the hydrogen sulfide atmosphere in an alkaline solution. by aspirating said hydrogen sulfide contaminated air through an aqueous solution of an alkali metal hydroxide which at the same time absorbs and becomes weaker by means of the carbon dioxide normally present in the air, and on account of the extreme dilution of the air to be treated as to hydrogen sulfide content, and hence minute traces of the latter present, this method has been found unsatisfactory.

In another process, the atmosphere leaving the spinning room has been treated with sulfur dioxide gas, and this method has proven ineffectual probably due to the extreme dilution and consequent low reaction velocity. In tests made by us in connection with the possible application of this method to factory usage, characteristic analytical tests were obtained by us for both hydrogen sulfide and sulfur dioxide in the exit gases from the system of treatment.

In still another system, it has been tried to render innocuous the hydrogen dioxide evolved by aspirating or otherwise leading the air containing the gas through certain aqueous solutions of oxidizing mediums such as potassium permanganate, potassium bichromate or sodium thiosulfate in various concentrations, but with indifferent results. The major portions of the methods heretofore proposed and known to us, have failed primarily due to the fact that it was necessary to work with extremely high dilutions of hydrogen sulfide.

In the usual method of viscose manufacture, the cellulose, either from wood or cotton or both in admixture, is treated with a desired amount of aqueous sodium hydroxide solution at a desired temperature and concentration for the period desired, a portion of the sodium hydroxide solution expressed until the resulting cake has the weight required, and these cakes then broken up into small particles or crumbs by means of mechanical treatment.

The crumbs are then usually placed in tight containers and left in a room under governed atmospheric and temperature conditions for a definite period, when they are placed in a drum or container and slowly rotated while the desired amount of carbon bisulfide is introduced. Rotation is usually continued until by means of either a chemical test applied to a previous batch or by the development of a certain carrot color, xanthation is considered to have been satisfactorily completed, when the contents of the drum are then thinned with aqueous so-' dium hydroxide solution, and run into receptacles where they remain a number of hours under controlled conditions and until the contents are considered optimum for spinning or film manufacturing purposes. The viscose solution, aged to the desired degree is then projected through orifices into a. liquid precipitating bath, the bath being usually of an acidic character in order to overcome the alkalinity of the viscose solution before precipitation. The precipitated filaments are then washed free from acid and until coagulation which proceeds from the periphery to the center of the individual filament has been completed, when the re actant-frced filaments are then further treated, but at the point where the filaments are considered free from reactants and sufficiently washed. substantially all of the hydrogen sulfide has been given off. and there is no further evolution of toxic gases.

As to the chemistry of the process, important in consideration of the merits of our invention, the process of manufacture as above outlined-is followed in all of its essentials. Upon the introduction of the desired amount of carbon hisulfide to the alkali cellulose in the slowly rotating drum. at the close of the addition of carbon bisulfide and the development of the desired color in the xanthated mass in the drum. there is present therein in addition to water, sodium hydroxide which has passed through the process as such up to this point, xanthated cellulose (alkali cellulose xanthate or sodium cellulose xanthate), sodium trithiocarbonate,

' evolution and removal of hydrogen sulfide comprising one of the primary objects of this invention, the compounds present in the Xanthated cellulose mixture in the drum, of the above named compounds, and which break down with the evolution of hydrogen sulfide in the normal spinning operation after precipitation or coagulation are sodium v above reaction is assumed ly present trithiocarbonate, sodium sulfide, sodium hydrogen sulfide, sodium dithiocarbonate, and sodium monothiocarbonate, of which by far the most important compound in this connection, is sodium trithiocarbonate.

In a typical reaction, under the conditions of treatments as herein stated, the sodium trithiocarbonate may be said to break down in accordance with the following reaction:

That is, sodium trithiocarbonate, plus the reagent (acid or acid anhydride) plus water already present, equals the sodium salt of the corresponding acid used (Whichin the to be a monobasic acid as shown by one atom of Na), plus 'hydrogen sulfide, plus carbon bisulfide.

Any acid or acid anhydride may be used which decomposes the sodium trithiocarbonate and related bodies and which is not detrimental to the viscose made therefrom. An example of such acid anhydride is CO the anhydride of carbonic acid (H 00 and substituting carbon dioxide for X 'in the above type reaction, the same would read Na CS CO H O=Na CO +H S CS where sodium trithiocarbonate plus carbon dioxide in the presence of the water normaltherein, gives sodium carbonate, hydrogen sulfide and carbon bisulfide.

It is hardly necessary to state that in addition to the chemicals mentioned as components of the crude xanthating mixture in the drum, are carbon bisulfide in small amounts both as the liquid form and in the gaseous condition.

WVe will now give a typical example of carrying our process into effect, it being understood that the amounts herein stated are for illustrative purposes only, and may be varied within wide limits without departing from the spirit and essence of our invention.

This treatment with any inorganic or organic acid or acid anhydride which will decompose sodium trithiocarbonate and still not harm the viscose made therefrom, may take place at any stage of the manufacture of viscose from the point of formation of raw viscose in the Xanthating drum up to the point where the viscose solution is considered in the proper condition for spinning purposes, but in the example given herein, the process will be described as carried out in the Xanthating introduction of the carbon bisulfide and after the proper color of the mass has been obtained. For simplicity in description, the acid or acid anhydride used, irrespective of its strength, but which preferably must be mechanically easy to manipulate and which does not decompose or otherwise deleteriously affect a substantial amount of the viscose made therefrom, will be spoken of as reagent.

After the Xanthation process in the drum has been completed and before the contents thereof have been thinned with sodium hydroxide solution preparatory to submission of the material to the ripening process, vacuum may be applied to eliminate air and excess of carbon bisulfide, and the gases issuing from the drum lead into a system for the decomposition of the carbon bisulfide, the vacuum being applied for about ten minutes, rotation of the contents of the drum being carried onmeanwhile. Then allow the reagent to slowly enter the drum still rotating, if the reagent is aliquid, preferably by means of a spraying or atomizer device, vacuum-having previously been turned off, the reagent beingintroduced comparatively slowly and in definite amount, the amount to be-introduced being usually determinable by the gradual disappearance-of the characteristic carrot color of the contents of the drum, and being replaced by a color which may be described as buff or light straw, as

seen through the peep window in the drum. The reagent decomposes the trithiocarbonate and other compounds with the evolution of hydrogen sulfide and carbon bisulfide, which gases as and when formed may be withdrawn by aspiration or otherwiseand into and through a system wherein the hydrogen sulfide and carbon bisulfide may be treated by alkali solution or otherwise by ways now known to combine or render innocuous the gases formed as the result of the breaking down of the sodium trithiocarbonate and related compounds.

The reagent, may consist of any acid oi acid anhydride having a hydrogen ion concentration constant of not greater than 18 1()-, which at the same time does not substantially decompose the xanthated cellulose. Carbon dioxide comes under the category of such an acid anhydride. It is readily procurable, relatively inexpensive drum at the close of the and being a gas, is easy to manipulate. Carbon dioxide decomposes trithiocarbonate, being the anhydride of a stronger acid, while carbon dioxide under the conditions of its use does not adversely affect the viscose produced therefrom.

If carbon dioxide be the reagent employed, the amount to be used may be gauged by the change in color of the contents of the drum after its admission thereto, but the amount required may also be determined approximately from the analytical data concerning the amount of by-products present, calculated as sodium trithiocarbonate, remembering that in a normal xanthation process the total combined sulfur in the drum at the close of xanthation in new viscose is about 2.3%, of which about 1.% is by-product sulfur in combination, and about 1.3% is sulfur in combination as xanthated" cellulose. If the process is to be applied at a stage of the ageing process, it is to be remembered that during ageing, or maturing of the viscose solution the by-product sulfur increases slightly, roughly some 0.3%, while the xanthate sulfur diminishes in percentage accordingly.

The gaseous products of reaction caused by decomposition from the introduction of CO or other reagent, may be removed from the drum by means of applying a vacuum, and the gases sweptinto a suitable absorption device containing waste caustic soda from the mercerization treatment of the cellulose, or black liquor from sulfite wood pulp manufacture, or oxidizing. reagents such as of the order ofthose above mentioned.

lVhatwe claim and desire to secure by Letters Patent is:

1. A process for sulfide gases from evolved incident to and the washing the removal of hydrogen viscose solutions normally the coagulationof viscose thereof, comprising removing said gases in a concentrated viscose solution prior to the precipitation of the same by decomposition of said bodies by means of an acid or acid anhydride mechanically easy to manipulate, which will decompose sodium trithiocarbonate without adversely af fccting the viscose made from such solutions so treated, aspirating the hydrogen sulfide and carbon bisulfide into an apparatus containing a suitable absorbing medium, and then allowing the process of viscose formation. precipitation and other steps to proceed in the usual manner as herein set forth.

2. A process for the removal of poisonous gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, comprising removing said products in the unripened viscose by decomposition of sodium trithiocarbonate by means of an acid or acid anhydride having a hydrogen ion concentration than 18 X 10- of not greater which'will decompose alkaline trithiocarbonate and still not adversely affect the quality of viscose produced, drawing the gases of decomposition into an apparatus containing an alkaline hydroxide solution, and then allowing the process of viscose formation, preclpitation and other steps to proceed in the usual manner as herein set forth.

3. A process for the removal of hydrogen sulfide gases from viscose solutions normally 7- evolved incident to the coagulation of viscose and the washing thereof, comprising removing said gases in the viscose solution before spinning, by decomposition of said bodies by means of solutions from which the poisonous gases have been removed by this treatment, aspirating the hydrogen sulfide and carbon bisulfide into an apparatus containing a solution containing sodium hydroxide, and then allowing the process of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

4. A process for the removal of poisonous gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, comprising removing hydrogen sulfide prior to coagulation of the viscose by decomposition of these bodies in a closed container, and normally present in the precipitation and washing operations incident to usual viscose filament for- .mation, by decomposition of sodium trithiocarbonate by means of carbon dioxide, drawing the gases of decomposition into an apparatus containing a solution containing an oxidizing agent, and'then allowing the process of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

5. A. process for the removal of hydrogen 1o; sulfide gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, comprising removing said gases in a concentrated viscose solution prior to the precipitation of the same, by decomposition of said bodies by means of an acid or acid anhydride mechanically easy to n'ianipulate, which will decompose sodium trithiocarbonate without adversely affecting the viscose made from such solutions so treated, aspirating the hydrogen sulfide and carbon bisulfide into an apparatus containing a suitable absorbing medium, and then allowing the process-of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

6. A process for the removal of poisonous gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, comprising removing said products in the unripened viscose, by decomposition of sodium trithioc'arbonate by means of an acid or acid anhydride having a hydrogen ion concentration of not greater than 18x10" which will decompose alkaline trithiocarbonate and still not adversely att'ect the quality of viscose produced, drawing the gases of decomposition into an apparatus containing an alkaline hydroxide solution, and then allowing the process of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

7 A process for the removal of hydrogen sulfide gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, comprising removing said gases in the viscose solution before spinning, by decomposition of said bodies by means of solutions from which the poisonous gases have been removed by this treatment, aspirating the hydrogen sulfide and carbon bisulfide into an apparatus containing a solution containing sodium hydroxide, and then allowing the process of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

8. A process for the removal of hydrogen sullide gases from viscose solutions normally evolved incident to the coagulation of viscose and the washing thereof, con'iprising removing hydrogen sulfide prior to coagulation of the viscose by decomposition of those bodies in a closed container, and normally present in the precipitation and washing operations incident to usual viscose filament formation, by decomposition of sodium trithiocarbonate by means of carbon dioxide, drawing the gases of decomposition into an apparatus containing a solution containing an oxidizing agent, and then allowing the process of viscose formation, precipitation and other steps to proceed in the usual manner as herein set forth.

9. A process for the removal of hydrogen sulfide and carbon bisulfide from viscose solutions before said viscose solutions have been coagulated and washed, comprising treating the viscose solution in any stage of manufacture between the formation of the raw viscose solution up to the ageing point where it is ready for filament formation and precipitation, by adding to said viscose solu tion in a closed container such as the container in which the original Xanthation was conducted. of an amount of carbon dioxide gas until the decomposable sulfurcompounds in the viscose solution, such as sodium trithiocarbonatc, have been decomposed, pass ing the products of decomposition through an aspirating systeminto a solution of alkali hydroxide to neutralize and render innocuous such gases given off, then allowing the normal process of viscose formation, precipitation, washing and spinning to take place in the usual manner, as set forth herein.

FREDERICK C. NIEDERHAUSER. HAYDEN B. KLINE. 

